A single state license authorizes the nurse to practice only in the state that issued the license.
A multi-state license authorizes the nurse to practice in other states that are part of The Nurse Licensure Compact (NLC) unless that privilege is otherwise restricted. If the nurse's home state is part of the NLC they may have a multi-state license.
Please refer to the information on the NCSBN website regarding Nurse Licensure Compacts or contact your board of nursing.